Endophytic Fungi as a Biological Control Agent for Soybean (Glycine max L. Merr) Pathogens

Soybeans (Glycine max (L. Merr)) are grown on 77 million acres in the United States with an estimated value of $39 billion. Yields are reduced by 10–20% annually due to fungal, viral, and bacterial diseases. Diseases are typically managed by host resistance, agronomic techniques, or pesticides, but none of these methods result in complete disease control. Biological control is another potential method that has not been readily investigated in soybeans.  Endophytic fungi are are able to colonize a plant asymptomatically, and have been shown to reduce pathogen growth in cacao. The role of endophytes within soybean is unknown, and therefore, we determined whether soybean endophytes prevented growth of two soybean pathogens: Sclerotinia sclerotiorum and Diaporthe phaseolorum. Interactions between endophytic and pathogenic fungi were analyzed by placing equivalent amounts of one of 34 various endophytic fungi and one of the aforementioned pathogenic fungi on potato dextrose agar. Each pathogen-endophyte combination was evaluated in a series of three replicate experiments. Experiments were evaluated for the endophytes potential to prevent growth by either antibiosis and competition, and observations were made every 4 days for two weeks.  Growth of D. phaseolorum and S. sclerotiorum was prevented by 27% and 15% of endophytes, respectively. Antibiosis was a more common form of antagonism, with 9% and 12% of endophytes preventing growth of D. phaseolorum and S. sclerotiorum, respectively. Endophytes that outcompeted pathogens were less common, with only 6% of endophytes able to outcompete D. phaseolorum and no endophytes able to outcompete S. sclerotiorum. Five endophytes prevented growth of both pathogens. The endophytes that showed the greatest potential to prevent pathogen growth will be investigated in planta.